Alicat EPCD Series Panduan Pengoperasian - Halaman 10

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The PD2I algorithm is a PID algorithm used primarily for high performance
pressure and flow control applications. It exhibits two basic differences from the
PD algorithm that most controllers utilize.
1. Instead of applying a damping function based upon the rate of change of the
process value, it applies a damping function based upon the square of the rate of
change of the process value.
2. The damping function is applied directly to the proportional error term before
that term is used in the proportional and integral functions of the algorithm.
This provides a certain amount of 'look ahead' capability in the control loop.
Because of these differences, you will note the following:
1. Increasing 'P' gain can be used to damp out overshoot and slow oscillations in
pressure controllers. You will know that 'P' gain is too high, when the controller
breaks into fast oscillations on step changes in setpoint. On flow controllers,
too low a 'P' gain results in slower response times. Too high a 'P' gain results in
overshoot and/or slow oscillation. A good starting value for 'P' gain is 200.
2. If the unit was originally shipped with the PD2I algorithm selected, the 'D' gain
value should be left at or near the factory setting because it relates primarily to
the system phase lags. If you are changing from the default algorithm to the PD2I
algorithm, you should start with a 'D' gain value of 20.
3. The 'I' gain is used to control the rate at which the process converges to the
setpoint, after the initial step change. Too low a value for 'I' gain shows up as a
process value that jumps to near the setpoint and then takes awhile to converge
the rest of the way. Too high a value for 'I' gain results in oscillation. A good
starting value for the 'I' gain is 200.

MAINTENANCE AND RECALIBRATION

General: EPC and EPCD-Series controllers require minimal maintenance. The single
most important thing that affects the life and accuracy of these devices is the
quality of the gas being measured. The instruments are designed to measure clean,
dry, non-corrosive gases.
Recalibration: The EPC device is an OEM product calibrated to NIST traceable
standards at the time of manufacture. As an OEM device there is not a factory
recommended periodic recalibration cycle. Recalibration can be requested at the
user's discretion/requirement. Before calling to schedule a recalibration, please
note the serial number on the back of the device.
Cleaning: EPC and EPCD-Series controllers require no periodic cleaning. If
necessary, the outside of the controller can be cleaned with a soft dry cloth.
Avoid excess moisture or solvents.
For repair, recalibration or recycling of this product, contact:
Alicat Scientific, Inc.
7641 N Business Park Drive
Tucson, Arizona 85743
USA
Ph. 520-290-6060
Fax 520-290-0109
Web site: www.alicat.com
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